1. Field of the Invention
The present invention relates to a motor for a power steering device and a power steering device using this motor for reversing the direction of the rotation of the motor and transmitting the reversed rotation to a pinion shaft via an output shaft.
2. Description of Related Art
Recently, as a power steering for a vehicle, an electrically driven power steering device using an electric motor, rather than a hydraulic motor, is used. In the prior art, the torque of a motor is required to be transmitted in the same rotational direction as the rotational direction of the steering wheel of a vehicle, and the armature of a motor is likewise rotated in the same direction as the rotation of the steering wheel as disclosed in Japanese unexamined patent application publication No. H6-316270.
However, this device has a problem in that when the flow of electric current to the motor is required to be switched so as to rotate the motor in the same direction as the rotation of a steering wheel, measures to suppress armature reaction and spark noise generation are required. This is because excessive current flows when the flow of current is switched. Further, a plurality of diodes and transistors for switching the flow direction of current are required.
One way of dealing with such problem is disclosed in Japanese unexamined patent application publication No. H7-61362, which shows a movable body that is straight spline-coupled to either one of a stub axle or a pinion shaft and helical spline-coupled to the other stub axle or the shaft; and a first or second clutch mechanism that is operated by the movable body moved by the rotation of the stub axle. The unidirectional rotation of a motor is reversed by a driving bevel gear and a pair of driven bevel gears, and is transmitted to the pinion shaft.
However, this device has a problem in that the life and the precision of a torsion bar are easily deteriorated. The reasons for such deterioration are (1) torque for moving the movable body via the helical spline coupling carried out by twisting the torsion bar provided between the stub axle and the pinion shaft through the rotation of the motor, is not required to be reversed; and (2) transmitting the rotation of the motor is directly applied to the torsion bar via the helical spline coupling.